Abstract
Changes in the light spectrum elicit responses in development and secondary metabolite biosynthesis and storage. The aim of this study was to determine the effect of two light sources on the physiological and yield parameters of three varieties of C. sativa cultivated under greenhouse conditions. The non-psychoactive varieties Calotoweed, Higthcol, and Souce Cauca were treated with two light sources [LED1(100% white) and LED2 (90% red, 8% blue, <1% far red)] during the vegetative phase. Under LED2, reductions in plant height (4%-26.7%), leaf area (21%-55%), and shoot dry mass (1.9%-30.3%) were observed; however, there was a higher distribution of biomass towards the inflorescences (40.1%-51.6%). No effect of the light type on the relative chlorophyll content was observed. In all three varieties grown under LED2, reductions in stomatal conductance (4.7%-27.4%), quantum efficiency of PSII (1%-11.7%), and electron transport rate (9.2%-15.8%) were observed compared to plants under LED1. There were no significant differences in dry flower yield between light types used or varieties. Under LED1, higher CBD contents (11.9%-13.4%) and CBD per gram of inflorescence (12.9 CBD g/inflorescence – 13.8 CBD g/inflorescence) were observed compared to LED2. Under LED2, the Calotoweed (0.5%) and Soucecauca (0.6%) varieties showed higher THC concentrations compared to plants under LED1. These results demonstrate that LED2 modified canopy architecture, resulting in more compact plants with greater biomass accumulation in the inflorescence; however, these plants exhibited limitations in photosynthetic performance, which decreased CBD production and increased THC production. In conclusion, the type of light not only modified plant architecture but also affected photosynthetic performance and the production of CBD and THC.
